Although there was an overall correspondence in temperature
effect on photosynthetic rate and growth rate, the photosynthetic
rates were much more sensitive to increasing temperature. The
optimal temperature for plant growth is usually lower than for
photosynthesis as photosynthesis is only one of several factors
determining growth (Körner, 1991). Hence, accelerating losses due
to faster increase in dark respiration relative to photosynthesis
at high temperature will lower the diurnal production and hence
contribute to the lower growth rates. But also elevated leaking of
dissolved organic matter from roots, faster leaf senescence and
changes in carbon allocation may be involved. Root allocation,
however, was highest at low temperatures and therefore did not
contribute to the measured differences in growth and photosynthetic
rates.